The present invention relates to a drill bit. More particularly, but not exclusively, it relates to an exchangeable drill bit for use with an electrically-powered hand drill to form holes in wood or similar materials.
It is well known for drill bits to have substantially cylindrical proximal ends adapted to be inserted into a drill chuck. It is also known to provide drill bits that have proximal ends which are non-cylindrical. (The proximal end, known as the ‘shank’, is the part of a drill bit gripped by the chuck of a drill). Different types of shank/chuck combination deliver different balances of performance, such as allowing higher torque or greater centering accuracy. Known shank types include the brace, straight, hex, triangle and moss taper shaped shanks Many of these are adapted for insertion into complementary drill chucks only.
Traditionally, using a drill bit simply required selecting a shank, which was inserted into a hole in the end of the drill. Over time, various more specialised chuck designs were developed, and modern chucks can grasp and drive some shanks more effectively than others. Such effectiveness is usually quantified in terms of the relative amount of power from the drill motor that is usefully transferred to the bit in the form of actual torque.
It is known, for example from U.S. Pat. No. 4,107,949 and Japanese Patent Application No. 62074510, to provide a shank having what is now known as an “SDS fitting”, which is connectable to an “SDS” chuck. (The claimed meaning of the initials SDS varies from manufacturer to manufacturer, and according to the language used). Drill bits having an SDS shank have the advantage that the SDS chuck has a spring-loaded locking mechanism, so that bits can be chucked with a simple and quick hand action. The SDS shank and chuck are particularly suited to hammer drilling in stone and concrete. The drill bit is not held solidly in the chuck, but can slide back and forth longitudinally, like a piston. The hammer of the drill acts to accelerate only the drill bit itself, and not the larger mass of the chuck, which makes hammer drilling with an SDS shank drill bit much more productive than with other types of shank. SDS shanks are therefore widely employed on masonry drill bits for which hammer drilling action is required.
Note: several variants of the SDS chuck design are known, for example under the designations SDS; SDS plus/SDS+; SDS-Top; and SDS-max. The principles of action of these are all substantially the same, the differences mainly being in dimensions and proportions. The term SDS hereinafter should therefore be understood to refer equally to SDS, SDS+, SDS-Top, SDS-max and any other such drill bit connecting arrangement operating on the same principles.
Wood drill bits for forming larger holes, such as the spade or paddle drill bit, are traditionally intended for delicate, careful work in joinery or cabinetmaking, and have simple shanks and thin shafts. They are not designed to undergo high torques or stresses, and have changed little since those bits used with hand-powered drills or in a bit and brace. However, there are many circumstances in which a tradesman or a DIY operator might wish to cut relatively large holes in wood, but with speed being a significant requirement.
It is hence an object of the present invention to provide a drill bit that is suitable for forming holes through wood and similar materials but is easier to fit into a drill and to exchange for another bit than is the case for current wood drill bits. It is also an object to provide such a drill bit that is more robust and more convenient in use than current wood bits.